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  #1  
Old 12-05-2011, 10:28 AM
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Default Electric Porsche

After 10 years, I'm finally able to begin my electric car conversion. My goals are 0-60 MPH in < 8 seconds, 100 mile range (60 is an absolute min) at 80% dod, >80 mph top speed, and 4 seats.

I've narrowed the donor car decision down to two: Porsche 944 or Porsche 911/912. I would prefer the 911, but not at the price they seem to be selling for in my area, $14 -20 k USD (1978-1989). The 944 goes for between $1,000 - $5,000 (1983-1987).

For components I don't think I will stray too far from what a lot of people have been doing:
9 inch Warp - keeping the clutch and flywheel
Soliton Jr, or Soliton1
56 cells at 130 aH CALB or 48 cells at 180 aH
Manzanita 20 - The idea of long recharging times (12 hours) doesn't bother me
Battery monitoring and instrumentation - not selected yet

I'm thinking that the batteries will be the system bottleneck and any money I can squeeze from the bugdet should go there. Not sure how many will fit without messing up the weight distribution too much.
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  #2  
Old 12-05-2011, 10:48 AM
steven4601 steven4601 is offline
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Default Re: Electric Porsche

Top tip, wait until a Porsche boxter engine blows. They are driven usually quite hard and failure rate is high enough to find them. This could help with keeping donor costs low.
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Old 12-05-2011, 11:29 AM
Rational Rational is offline
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Default Re: Electric Porsche

Quote:
Originally Posted by Joey View Post
100 mile range
Using the method here,
http://physics.ucsd.edu/do-the-math/...g-on-gasoline/
and just accounting for air drag, to go 100 miles at 33 mph using the vehicle cross section and drag coefficient in the link you'll need 2200 w-h.
At 67 mph you'll need 8800.

0.3 =Cd
3 =A, cross sectional area, m^2
1.3 =p, air density in kg/m^3
30 =v, velocity, m/s
60000 =D, distance traveled, meters
E=0.5(Cd)pAD(v^2)
31590000 =calc'd E, energy, in joules
8775 =calc'd E, energy in w-h

The energy used to cancel out Rolling Resistance is another calculation, as is your accel requirement, as is your top speed.
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  #4  
Old 12-05-2011, 11:52 AM
DavidDymaxion DavidDymaxion is offline
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Default Re: Electric Porsche

The 911 is a great choice of car! I'll admit my bias, I have one that I have converted (actually am converting). The 2.7 motor had issues, so you can get those a bit cheaper. I found one with a blown motor but very good condition otherwise. The rear seats are pretty small and don't have seat belts (at least for my old one). 1977+ is nice because they were fully galvanized and much less rust prone. The 912 is basically the same car and much cheaper.

Here are a few details on mine:

http://ExplodingDinosaurs.com

Quote:
Originally Posted by Joey View Post
After 10 years, I'm finally able to begin my electric car conversion. My goals are 0-60 MPH in < 8 seconds, 100 mile range (60 is an absolute min) at 80% dod, >80 mph top speed, and 4 seats.

I've narrowed the donor car decision down to two: Porsche 944 or Porsche 911/912. I would prefer the 911, but not at the price they seem to be selling for in my area, $14 -20 k USD (1978-1989). The 944 goes for between $1,000 - $5,000 (1983-1987).

For components I don't think I will stray too far from what a lot of people have been doing:
9 inch Warp - keeping the clutch and flywheel
Soliton Jr, or Soliton1
56 cells at 130 aH CALB or 48 cells at 180 aH
Manzanita 20 - The idea of long recharging times (12 hours) doesn't bother me
Battery monitoring and instrumentation - not selected yet

I'm thinking that the batteries will be the system bottleneck and any money I can squeeze from the bugdet should go there. Not sure how many will fit without messing up the weight distribution too much.
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  #5  
Old 12-05-2011, 02:09 PM
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Default Re: Electric Porsche

Quote:
Originally Posted by Rational View Post
Using the method here,
http://physics.ucsd.edu/do-the-math/...g-on-gasoline/
and just accounting for air drag, to go 100 miles at 33 mph using the vehicle cross section and drag coefficient in the link you'll need 2200 w-h.
At 67 mph you'll need 8800.

60000 =D, distance traveled, meters
Thanks for the link. I think D should be 160000 meters (= 100 miles). Then the needed energy is 23500 for 100 miles, or 235 watt hours / mile.

I was estimating 250 watt hours / mile based on results for other porsches posted in the garage and on EVAlbum.

For a series pack:
Energy = S*C*V

with S = 48 cells
C = 180 amp hr cell capacity
and V = 3.2

I get 27650 watt hours.

If I multiply pack energy by 80% dod, and divide by 250 watt hours/mile, I estimate 88 mile range.

This safely meets my minimum range requirement of 60 mile, and my goal of 100 miles could be feasible at lower speeds (62 MPH) or with more cells (55).

These calculations assume a lot (like level terrain, constant velocity without starts and stops, low friction losses, etc) and I'm only considering then as a general guideline.
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  #6  
Old 12-05-2011, 02:11 PM
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Default Re: Electric Porsche

Quote:
Originally Posted by steven4601 View Post
Top tip, wait until a Porsche boxter engine blows. They are driven usually quite hard and failure rate is high enough to find them. This could help with keeping donor costs low.
I've waited 10 years already. I can wait a little longer to get a good deal. I do need 4 seats though, so the boxter and 914 are out.
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  #7  
Old 12-05-2011, 02:15 PM
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Default Re: Electric Porsche

Quote:
Originally Posted by DavidDymaxion View Post
The 911 is a great choice of car! I'll admit my bias, I have one that I have converted (actually am converting). The 2.7 motor had issues, so you can get those a bit cheaper. I found one with a blown motor but very good condition otherwise. The rear seats are pretty small and don't have seat belts (at least for my old one). 1977+ is nice because they were fully galvanized and much less rust prone. The 912 is basically the same car and much cheaper.

Here are a few details on mine:

http://ExplodingDinosaurs.com
I love the shape and style of the 911, and I agree on the rust protection. The plan is to be a daily driver, and while we don't have salt on the road, we do get 37 inches of rain a year. If I could get one for $10,000 in good shape I would have to do it.
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  #8  
Old 12-05-2011, 02:29 PM
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Default Re: Electric Porsche

I'd love a 911, but budget gave me a 944. If you go that way get the 85.5+ the interior is just so much nicer. The 944 is still a nice car, and nice to work on (once the gas stuff is gone) not a single rusted bolt, many lightweight parts. Plenty of original and after market support for parts/upgrades. The transmission from a Turbo gives you nicer ratio's to use the high torque of an electric motor (assuming 1000A controller), as well as being a bit beefier to handle that torque long term. I'm using an A123 pack and it will all be in the rear, but there is plenty of room up front if you went with a larger prismatic pack and had to split it front/rear.
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  #9  
Old 12-05-2011, 02:43 PM
Rational Rational is offline
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Default Re: Electric Porsche

Quote:
Originally Posted by Joey View Post
Thanks for the link. I think D should be 160000 meters (= 100 miles). Then the needed energy is 23500 for 100 miles, or 235 watt hours / mile.
My bad. I used to know this stuff!

Fixed it

0.3 =Cd
3 =A, cross sectional area, m^2
1.3 =p, air density in kg/m^3
30 =v, velocity, m/s
161000 =D, distance traveled, meters
E=0.5(Cd)pAD(v^2)
84766500 =calc'd E, energy, in joules
23546.25 =calc'd E, energy in w-h
235.4625 =calc'd E in w-h/mile

Last edited by Rational; 12-05-2011 at 02:47 PM.
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  #10  
Old 12-05-2011, 11:35 PM
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Joey Joey is offline
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Default Re: Electric Porsche

It will be a 911 afterall. I put a deposit on one today after work. I'll pick it up tomorrow. It is a 1983 SC and the condition was very nice. Service records going back over the last 40,000 miles.
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